The present invention relates to new electron transport compounds and a photoconductor for electrophotography (hereinafter referred to as an xe2x80x9celectrophotographic photoconductorxe2x80x9d or simply as a xe2x80x9cphotoconductorxe2x80x9d). Specifically, the present invention relates to an electrophotographic photoconductor that includes a photosensitive layer of organic materials on an electrically conductive substrate which is used in printers and copying machines that employ electrophotographic techniques.
Conventional photoconductors for printers, facsimiles and copying machines using electrophotographic techniques include an inorganic photoconductive material such as selenium or alloys of selenium. Other inorganic photoconductive materials such as zinc oxide and cadmium sulfide dispersed in a resin binder have also been used. Recently, research and development has been performed to investigate the use of organic photoconductive materials in electrophotographic photoconductors. Some organic electrophotographic photoconductors exhibiting improved sensitivity and durability have been developed.
Photoconductors must retain surface charges in the dark, generate charges in response to received light and transport charges in response to the received light. The so-called single-layer-type photoconductor includes a layer that exhibits all the aforementioned functions. The so-called laminate-type photoconductor includes a laminate consisting of a layer that contributes to charge generation and a layer that contributes to surface charge retention in the dark and charge transport under light exposure.
Electrophotography using the aforementioned photoconductors can form images using, for example, the Carlson process. The Carlson process includes the steps of electrifying the photoconductor by corona discharge in the dark, forming electrostatic latent images of original letters and pictures by light irradiation onto the electrified photoconductor, developing the latent images with toner, and fixing (copying) the developed toner images on a carrier such as paper. After the toner images are copied, the charges on the photoconductor are removed, the residual toner is removed, the optical charge is removed and the photoconductor is prepared for the next image formation.
The organic photoconductors developed so far are superior to the inorganic photoconductors in flexibility, ease of film formation, low manufacturing costs and safety. Further improvements of the sensitivity and durability of the organic photoconductors have been studied using a variety of organic materials.
Most of the organic photoconductors are of a laminate-type which distributes the foregoing basic functions among a charge generation layer and a charge transport layer. Usually, the laminate-type photoconductor includes an electrically conductive substrate; a charge generation layer on the substrate, containing a charge generation agent such as pigment or dye; and a charge transport layer, containing a charge transport agent such as hydrazone and triphenylamine on the charge generation layer. Due to the electron donating nature of the charge transport agent, the laminate-type photoconductor is usually a hole-transport-type, which exhibits sensitivity when its surface is negatively electrified. The corona discharge for negative electrification is more unstable than that for positive electrification and generates ozone and nitrogen oxide. The ozone and nitrogen oxide that are generated, absorb to the photoconductor surface, resulting in deterioration of the photoconductor physically and chemically. The ozone and nitrogen oxide are also hazardous to the environment. The photoconductor of a positive-electrification-type is superior to the negative-electrification-type of photoconductor, since the positive-electrification-type photoconductor can be used in a greater variety of working conditions. The fields to which the positive-electrification-type photoconductor is applicable are wider.
Due to the limitations of the negative-electrification-type photoconductors, research has been done to develop photoconductors for positive electrification. For example, single-layer-type photoconductors has been proposed which includes a photosensitive layer where a charge generation agent and a charge transport agent are dispersed in a resin binder. Some of these are used practically. However, the single-layer-type photoconductor is not sensitive enough to be applicable to high-speed machines. In addition, the single-layer-type photoconductor must have sufficient stability during repeated use.
To improve sensitivity, a positive-electrification-type photoconductor has been proposed which has a function-separation-type laminate with a charge generation layer laminated on a charge transport layer. However, corona discharge, light irradiation and mechanical wear interfere with stability under repeated use, since this type of photoconductor has a charge generation layer in its surface. Placing a protection layer on the charge generation layer has been proposed to obviate the aforementioned problems. Although the protection layer improves mechanical wear resistance, it interferes with the ability to improve the electrical properties of the photoconductor, including sensitivity.
A positive-electrification-type photoconductor that includes a function-separation-type laminate of a charge transport layer containing an electron transport agent, on a charge generation layer, has also been proposed. The electron transport agent such as 2,4,7-trinitro-9-fluorenone is known to those skilled in the art. However, this electron transport agent is carcinogenic and hazardous to human health. Although other electron transport agents such as cyanine compounds and quinone compounds have been proposed (cf. Japanese Unexamined Laid Open Patent Applications No. S50-131941, No. H06-59483, No. H06-123986 and No. H09-190003), a compound exhibiting sufficient electron transport capability has not yet been obtained.
In view of the foregoing, it is an object of the invention to provide a new charge transport agent and a positive-electrification-type electrophotographic photoconductor that obviates the foregoing problems. It is another object of the invention to provide a positive-electrification-type electrophotographic photoconductor that contains the charge transport agent in its photosensitive layer and can be used in high-speed copying machines and printers.
The inventor of the present invention has examined various organic materials to achieve the foregoing objects. As a result of many experiments, the present inventor has found that a specific compound described by the general formula (I) in FIG. 3 or (II) in FIG. 4 is very effective in improving electrophotographic properties and in obtaining high sensitivity in positive-electrification-type photoconductors. The precise mechanism has not yet been well defined.
As used herein, the term xe2x80x9calkylxe2x80x9d is defined to include substituted or unsubstituted straight or branched carbon chains. An xe2x80x9carylxe2x80x9d group is defined as a substituted or unsubstituted carbocyclic or heterocyclic aromatic ring system. A substituent for a substituted alkyl, alkoxy or aryl group is defined to include one or more chemically feasible substituents that would be well known to one skilled in the art. Such substituents may include at least one of the following: a straight, branched or cyclic alkyl or alkenyl group, an alkoxy group, an alkoxycarbonyl group or a halogen atom.
Briefly stated, the present invention provides a new charge transport agent in a photosensitive layer of a positive-electrification-type electrophotographic photoconductor that can be used with high speed copying machines. The charge transport agent is described by the following general formula (I): 
wherein R1 and R2 are each independently a halogen atom, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms, an arylalkyl group, a substituted or unsubstituted aryl group or a residue for forming a ring. A1 is an oxygen atom, m is an integer from 0 to 4 and n is an integer from 0 to 5.
According to an aspect of the invention, a photoconductor for electrophotography is provided including: an electrically conductive substrate and a photosensitive layer on the electrically conductive substrate. The photosensitive layer contains a charge generation agent and a charge transport agent. The charge transport agent includes an electron transport compound described by the general formula (I) in FIG. 3; where R1 and R2 are each independently a halogen atom, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms, an arylalkyl group, a substituted or unsubstituted aryl group, or a residue forming a ring. A1 is an oxygen atom; m is 0, 1, 2, 3 or 4; and n is 0, 1, 2, 3, 4 or 5.
Advantageously, the R1 and R2 substituents are alkyl groups.
Advantageously, the R1 and R2 substituents are alkoxy groups.
Advantageously, the R1 and R2 substituents are aryl groups.
Advantageously, R1""s are identical to each other when m is 2 or more.
Advantageously, R1""s are different from each other when m is 2 or more.
Advantageously, R2""s are identical to each other for n of 2 or more.
Advantageously, R2""s are different from each other for n of 2 or more.
According to another aspect of the invention, a new charge transport compound in a photosensitive layer of a positive-electrification-type electrophotographic photoconductor is provided that can be used with high speed copying machines. The new charge transport agent is described by the following general formula (II): 
wherein R5, R6, R7 and R8 are each independently selected from the group consisting of a halogen atom and an alkyl group having from 1 to 8 carbon atoms; R9 and R10 are each independently selected from the group consisting of a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms and an aryl group; B1 and B2 are an oxygen atom; and o, p, q and r are each independently an integer from 0 to 4.
According to a further aspect of the invention, a photoconductor for electrophotography is provided including an electrically conductive substrate and a photosensitive layer on the electrically conductive substrate. The photosensitive layer contains a charge generation agent and a charge transport agent. The charge transport agent includes an electron transport compound described by the general formula (II) in FIG. 4; where R5 is a halogen atom, or an alkyl group having from 1 to 8 carbon atoms; R6 is a halogen atom, or an alkyl group having from 1 to 8 carbon atoms; R7 is a halogen atom, or an alkyl group having from 1 to 8 carbon atoms; R8 is a halogen atom, or an alkyl group having from 1 to 8 carbon atoms; R9 is a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, or an aryl group; R10 is a hydrogen atom, an alkyl group having from 1 to 8 carbon atoms, or an aryl group; B1 is an oxygen atom; B2 is an oxygen atom; o is 0, 1, 2, 3 or 4; p is 0, 1, 2, 3 or 4; q is 0, 1, 2, 3 or 4; r is 0, 1, 2, 3 or 4; R5""s are identical to or different from each other for o of 2 or more; R6""s are identical to or different from each other for p of 2 or more; R7""s are identical to or different from each other for q of 2 or more; and R8""s are identical to or different from each other for r of 2 or more.
Advantageously, the R5, R6, R7 and R8 substituents are alkyl groups.
Advantageously, the R9 and R10 substituents are aryl groups.
Advantageously, R5""s are identical each other for o of 2 or more.
Advantageously, R5""s are different from each other for o of 2 or more.
Advantageously, R6""s are identical to each other for p of 2 or more.
Advantageously, R6""s are different from each other for p of 2 or more.
Advantageously, R7""s are identical each other for q of 2 or more.
Advantageously, R7""s are different from each other for q of 2 or more.
Advantageously, R8""s are identical to each other for r of 2 or more.
Advantageously, R8""s are different from each other for r of 2 or more.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.